Driving a surgical instrument articulation

ABSTRACT

A robotic surgical instrument comprising: a shaft; an articulation at a distal end of the shaft for articulating an end effector, the articulation driveable by pairs of driving elements; and an instrument interface at a proximal end of the shaft, the instrument interface comprising an internal portion which is within the projected profile of the shaft and an external portion which is outside of the projected profile of the shaft, the instrument interface comprising instrument interface elements for driving pairs of driving elements, wherein a first instrument interface element engages a first pair of driving elements in the internal portion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit under 35 USC 119 of United KingdomApplication No. 1521812.6, filed Dec. 10, 2015. The contents of thisapplication is hereby incorporated by reference in its entirety.

BACKGROUND

It is known to use robots for assisting and performing surgery. FIG. 1illustrates a typical surgical robot 100 which consists of a base 108,an arm 102, and an instrument 105. The base supports the robot, and isitself attached rigidly to, for example, the operating theatre floor,the operating theatre ceiling or a trolley. The arm extends between thebase and the instrument. The arm is articulated by means of multipleflexible joints 103 along its length, which are used to locate thesurgical instrument in a desired location relative to the patient. Thesurgical instrument is attached to the distal end 104 of the robot arm.The surgical instrument penetrates the body of the patient 101 at a port107 so as to access the surgical site. At its distal end, the instrumentcomprises an end effector 106 for engaging in a medical procedure.

FIG. 2 illustrates a typical surgical instrument 200 for performingrobotic laparoscopic surgery. The surgical instrument comprises a base201 by means of which the surgical instrument connects to the robot arm.A shaft 202 extends between base 201 and articulation 203. Articulation203 terminates in an end effector 204. In FIG. 2, a pair of serratedjaws are illustrated as the end effector 204. The articulation 203permits the end effector 204 to move relative to the shaft 202. It isdesirable for at least two degrees of freedom to be provided to themotion of the end effector 204 by means of the articulation.

FIG. 3 illustrates an example of a known surgical instrument 300 inwhich end effector 204 is permitted to move relative to shaft 202 bymeans of pitch joint 301 and two yaw joints 302. Joint 301 enables theend effector 204 to rotate about pitch axis 303. Joints 302 enable eachjaw of the end effector 204 to rotate about yaw axis 304. The joints aredriven by cables 306, 307 and 308. Pulley 305 is used to direct cables307 and 308 from their passage over the pitch joint to the yaw joints.Pulley 305 is offset from the central axis of the articulation 203. Theexternal diameter of the shaft is 8 mm in order to accommodate thenumber, size and location of the internal elements of the articulatedportion.

It is desirable to reduce the external diameter of the instrument inorder to minimise the size of the incision through the skin of thepatient and minimise disruption inside the patient's body. It is alsodesirable to minimise the weight of the surgical instrument so as tominimise the size and weight of the robot base and arm required tosupport the instrument, thereby enabling the robot as a whole to be morecompact and hence occupy a smaller space in the operating theatre and bemore moveable within the operating theatre.

In a typical laparoscopy operation, a surgeon utilises many instruments,and hence exchanges one instrument for another many times. It istherefore desirable to minimise the time taken and maximise the easewith which one instrument is detached from a robot arm and a differentinstrument is attached. Additionally, it is desirable to minimise thetime taken in setting up the instrument ready for use once it has beenattached to the robot arm.

SUMMARY OF THE INVENTION

According to an aspect of the invention, there is provided a roboticsurgical instrument as set out in the accompanying claims.

BRIEF DESCRIPTION OF THE FIGURES

The present invention will now be described by way of example withreference to the accompanying drawings. In the drawings:

FIG. 1 illustrates a surgical robot performing a surgical procedure;

FIG. 2 illustrates a known surgical instrument;

FIG. 3 illustrates a known arrangement of an articulated end effector ofa surgical instrument;

FIG. 4 illustrates a surgical robot;

FIGS. 5A and 5B illustrate a distal end of a surgical instrument;

FIGS. 6A and 6B illustrate a pulley arrangement of the distal end of thesurgical instrument of FIGS. 5A and 5B in a straight configuration;

FIGS. 7A-7E illustrate a pulley arrangement of the distal end of thesurgical instrument of FIGS. 5A and 5B in a variety of non-straightconfigurations;

FIG. 8 illustrates the offset pulleys of the pulley arrangement shown inFIGS. 5A and 5B;

FIGS. 9A-9D illustrate non-straight configurations of the distal end ofa surgical instrument;

FIG. 10 illustrates a supporting body and redirecting pulleys of thearticulation of a surgical instrument;

FIGS. 11A and 11B illustrate a different view of the supporting body andredirecting pulleys of FIG. 10;

FIGS. 12 and 13 illustrate the supporting body of the articulation ofFIGS. 10 and 11 in isolation;

FIG. 14 illustrates a spindle mounted redirecting pulley mounted to thesupporting body of FIGS. 12 and 13;

FIG. 15 illustrates a bevelled surface and groove of the supporting bodyof FIGS. 12 and 13;

FIGS. 16A and 16B illustrate arrangements of driving elements in aninstrument shaft;

FIGS. 17A and 17B illustrate two views of a surgical instrument;

FIG. 18 illustrates spokes in an instrument shaft;

FIGS. 19A, 19B and 19C illustrate three views of an instrumentinterface;

FIGS. 20A and 20B illustrate tensioning mechanisms;

FIGS. 21A, 21B and 21C illustrate three views of a drive assemblyinterface of a robot arm;

FIGS. 22A, 22B and 22C illustrate configurations of an instrumentinterface element;

FIG. 23 illustrates a configuration of a drive assembly interfaceelement;

FIG. 24 illustrates an instrument interface engaged in a drive assemblyinterface; and

FIG. 25 illustrates a further view of an instrument interface.

DETAILED DESCRIPTION

FIG. 4 illustrates a surgical robot having an arm 400 which extends froma base 401. The arm comprises a number of rigid limbs 402. The limbs arecoupled by revolute joints 403. The most proximal limb 402 a is coupledto the base by joint 403 a. It and the other limbs are coupled in seriesby further ones of the joints 403. Suitably, a wrist 404 is made up offour individual revolute joints. The wrist 404 couples one limb (402 b)to the most distal limb (402 c) of the arm. The most distal limb 402 ccarries an attachment 405 for a surgical instrument 406. Each joint 403of the arm has one or more motors 407 which can be operated to causerotational motion at the respective joint, and one or more positionand/or torque sensors 408 which provide information regarding thecurrent configuration and/or load at that joint. Suitably, the motorsare arranged proximally of the joints whose motion they drive, so as toimprove weight distribution. For clarity, only some of the motors andsensors are shown in FIG. 4. The arm may be generally as described inour co-pending patent application PCT/GB2014/053523.

The arm terminates in an attachment 405 for interfacing with theinstrument 406. Suitably, the instrument 406 takes the form describedwith respect to FIG. 2. The instrument has a diameter less than 8 mm.Suitably, the instrument has a 5 mm diameter. The instrument may have adiameter which is less than 5 mm. The instrument diameter may be thediameter of the shaft. The instrument diameter may be the diameter ofthe profile of the articulation. Suitably, the diameter of the profileof the articulation matches or is narrower than the diameter of theshaft. The attachment 405 comprises a drive assembly for drivingarticulation of the instrument. Movable interface elements of the driveassembly interface mechanically engage corresponding movable interfaceelements of the instrument interface in order to transfer drive from therobot arm to the instrument. One instrument is exchanged for anotherseveral times during a typical operation. Thus, the instrument isattachable and detachable from the robot arm during the operation.Features of the drive assembly interface and the instrument interfaceaid their alignment when brought into engagement with each other, so asto reduce the accuracy with which they need to be aligned by the user.

The instrument 406 comprises an end effector for performing anoperation. The end effector may take any suitable form. For example, theend effector may be smooth jaws, serrated jaws, a gripper, a pair ofshears, a needle for suturing, a camera, a laser, a knife, a stapler, acauteriser, a suctioner. As described with respect to FIG. 2, theinstrument comprises an articulation between the instrument shaft andthe end effector. The articulation comprises several joints which permitthe end effector to move relative to the shaft of the instrument. Thejoints in the articulation are actuated by driving elements, such ascables. These driving elements are secured at the other end of theinstrument shaft to the interface elements of the instrument interface.Thus, the robot arm transfers drive to the end effector as follows:movement of a drive assembly interface element moves an instrumentinterface element which moves a driving element which moves a joint ofthe articulation which moves the end effector.

Controllers for the motors, torque sensors and encoders are distributedwith the robot arm. The controllers are connected via a communicationbus to control unit 409. A control unit 409 comprises a processor 410and a memory 411. Memory 411 stores in a non-transient way software thatis executable by the processor to control the operation of the motors407 to cause the arm 400 to operate in the manner described herein. Inparticular, the software can control the processor 410 to cause themotors (for example via distributed controllers) to drive in dependenceon inputs from the sensors 408 and from a surgeon command interface 412.The control unit 409 is coupled to the motors 407 for driving them inaccordance with outputs generated by execution of the software. Thecontrol unit 409 is coupled to the sensors 408 for receiving sensedinput from the sensors, and to the command interface 412 for receivinginput from it. The respective couplings may, for example, each beelectrical or optical cables, or may be provided by a wirelessconnection. The command interface 412 comprises one or more inputdevices whereby a user can request motion of the end effector in adesired way. The input devices could, for example, be manually operablemechanical input devices such as control handles or joysticks, orcontactless input devices such as optical gesture sensors. The softwarestored in memory 411 is configured to respond to those inputs and causethe joints of the arm and instrument to move accordingly, in compliancewith a pre-determined control strategy. The control strategy may includesafety features which moderate the motion of the arm and instrument inresponse to command inputs. Thus, in summary, a surgeon at the commandinterface 412 can control the instrument 406 to move in such a way as toperform a desired surgical procedure. The control unit 409 and/or thecommand interface 412 may be remote from the arm 400.

FIGS. 5A and 5B illustrate opposing views of the distal end of asurgical instrument. In FIGS. 5A and 5B, the end effector 501 comprisesa pair of end effector elements 502, 503, which in FIGS. 5A and 5B aredepicted as a pair of opposing serrated jaws. It will be understood thatthis is for illustrative purposes only. The end effector may take anysuitably form, such as those described above. The end effector 501 isconnected to the shaft 504 by articulation 505. Articulation 505comprises joints which permit the end effector 501 to move relative tothe shaft 504. A first joint 506 permits the end effector 501 to rotateabout a first axis 510. The first axis 510 is transverse to thelongitudinal axis of the shaft 511. A second joint 507 permits the firstend effector element 502 to rotate about a second axis 512. The secondaxis 512 is transverse to the first axis 510. A third joint 513 permitsthe second end effector element 503 to rotate about the second axis 512.Suitably, the first end effector element 502 and the second end effectorelement 503 are independently rotatable about the second axis 512 by thesecond and third joints. The end effector elements may be rotated in thesame direction or different directions by the second and third joints.The first end effector element 502 may be rotated about the second axis,whilst the second end effector element 503 is not rotated about thesecond axis. The second end effector element 503 may be rotated aboutthe second axis, whilst the first end effector element 502 not rotatedabout the second axis.

FIGS. 5A and 5B depict a straight configuration of the surgicalinstrument in which the end effector is aligned with the shaft. In thisorientation, the longitudinal axis of the shaft 511 is coincident withthe longitudinal axis of the articulation and the longitudinal axis ofthe end effector. Articulation of the first, second and third jointsenables the end effector to take a range of attitudes relative to theshaft. FIGS. 9A-D illustrate some of the configurations of the distalend of the instrument in which articulation about all the first, secondand third joints has been driven relative to the straight configurationof FIGS. 5A and 5B.

Returning to FIGS. 5A and 5B, the shaft terminates at its distal end inthe first joint 506. The articulation 505 comprises a supporting body509. At one end, the supporting body 509 is connected to the shaft 504by the first joint 506. At its other end, the supporting body 509 isconnected to the end effector 501 by second joint 507 and third joint513. Thus, first joint 506 permits the supporting body 509 to rotaterelative to the shaft 504 about the first axis 510; and the second joint507 and third joint 513 permit the end effector elements 502, 503 torotate relative to the supporting body 509 about the second axis 512.

In the figures, the second joint 507 and third joint 513 both permitrotation about the same axis 512. However, the second and third jointsmay alternatively permit rotation of the end effector elements aboutdifferent axes. The axis of rotation of one of the end effector elementsmay be offset in the longitudinal direction of the shaft 504 from theaxis of rotation of the other end effector element. The axis of rotationof one of the end effector elements may be offset in a directiontransverse to the longitudinal direction of the shaft 504 from the axisof rotation of the other end effector element. The axis of rotation ofone of the end effector elements may not be parallel to the axis ofrotation of the other end effector element. The axes of rotation of theend effector elements 502, 503 may be offset in the longitudinaldirection of the shaft and/or offset in a direction perpendicular to thelongitudinal direction of the shaft and/or angled with respect to eachother. This may be desirable as a result of the end effector elementsbeing asymmetric. For example, in an electrosurgical element, a firstend effector element may be powered and a second end effector elementnot powered and insulated from the first end effector element. To aidthis, the axes of rotation of the two end effector elements may beoffset in the direction perpendicular to the longitudinal direction ofthe shaft. In another example, a first end effector element may be ablade and a second end effector element a flat cutting surface. To aiduse of the blade, the axes of rotation of the two end effector elementsmay be angled to one another.

The joints of the articulation are driven by driving elements. Thedriving elements are elongate elements which extend from the joints inthe articulation through the shaft to the instrument interface.Suitably, each driving element can be flexed laterally to its mainextent at least in those regions where it engages the internalcomponents of the articulation and instrument interface. In other words,each driving element can be flexed transverse to its longitudinal axisin the specified regions. This flexibility enables the driving elementsto wrap around the internal structure of the instrument, such as thejoints and pulleys. The driving elements may be wholly flexibletransverse to their longitudinal axes. The driving elements are notflexible along their main extents. The driving elements resistcompression and tension forces applied along their length. In otherwords, the driving elements resist compression and tension forces actingin the direction of their longitudinal axes. The driving elements have ahigh modulus. The driving elements remain taut in operation. They arenot permitted to become slack. Thus, the driving elements are able totransfer drive from the instrument interface to the joints. The drivingelements may be cables.

Suitably, each joint is driven by a pair of driving elements. Referringto FIGS. 5A and 5B, the first joint 506 is driven by a first pair ofdriving elements A1,A2. The second joint 507 is driven by a second pairof driving elements B1,B2. The third joint is driven by a third pair ofdriving elements C1,C2. Suitably, each joint is driven by its own pairof driving elements. In other words, each joint is driven by a dedicatedpair of driving elements. Suitably, the joints are independently driven.A pair of driving elements may be constructed as a single piece as shownfor the third pair of driving elements in FIGS. 5A and 5B. In this case,the single piece is secured to the joint at one point. For example, thethird pair of driving elements C1,C2 comprises a ball feature 520 whichis secured to the third joint 513. This ensures that when the pair ofdriving elements is driven, the drive is transferred to motion of thejoint about its axis. Alternatively, a pair of driving elements may beconstructed as two pieces. In this case, each separate piece is securedto the joint.

The surgical instrument of FIGS. 5A and 5B further comprises a pulleyarrangement around which the second and third pairs of driving elementsare constrained to move. The pulley arrangement is better illustrated inFIGS. 6A and 6B. The supporting body 509 is not shown in FIGS. 6A and 6Bin order to more clearly illustrate the pulley arrangement. The pulleyarrangement comprises a first set of pulleys 601. The first set ofpulleys 601 is rotatable about the first axis 510. Thus, the first setof pulleys 601 rotate about the same axis as the first joint 506. Thepulley arrangement further comprises a second set of pulleys 602. Thepulley arrangement further comprises a pair of redirecting pulleys 603.

The pulley arrangement is more clearly illustrated in FIGS. 7A-E. Thesupporting body, the first joint and the first pair of driving elementshave all been omitted from FIGS. 7A-E in order to more clearlyillustrate the pulley arrangement. The second set of pulleys comprises afirst pulley 701 and a second pulley 702. The first pulley 701 isrotatable about a third axis 703 which is parallel to the first axis510. The third axis 703 is offset from the first axis 510 both in thelongitudinal direction of the shaft and also transverse to thelongitudinal direction of the shaft. The second pulley 702 is rotatableabout a fourth axis 704 which is parallel to the first axis 510. Thefourth axis 704 is offset from the first axis 510 both in thelongitudinal direction of the shaft and also transverse to thelongitudinal direction of the shaft. The third and fourth axes areparallel but offset from each other. The third axis 703 and fourth axis704 are in the same plane perpendicular to the longitudinal direction ofthe shaft. FIG. 8 illustrates the distal end of the surgical instrumentfrom a different view which more clearly shows the offset axes of thefirst pulley 701 and the second pulley 702 of the second set of pulleys.By offsetting the first pulley 701 and the second pulley 702, thedriving element wrapped around each pulley is able to extend down theshaft after having wrapped around the pulley. As shown in FIG. 6A, thefirst pulley 701 and second pulley 702 of the second set of pulleys 602are located on opposing sides of the first joint 506 in a longitudinaldirection of the shaft 504. The first pulley 701 and second pulley 702are located on opposing sides of the first pair of driving elementsA1,A2.

The second set of pulleys is located between the first set of pulleysand the instrument interface end of the shaft. Suitably, the second setof pulleys is located within the shaft as shown in the figures.Alternatively, the second set of pulleys may be located within thearticulation between the first joint 506 and the second joint 507.However, by locating the second set of pulleys at the distal end of theshaft 508, the distance between the first and second joints is reducedcompared to the alternative arrangement in which the second set ofpulleys are located in the articulation, thereby reducing the stiffnessof the supporting body 509 required to maintain accurate positioning ofthe end effector 501.

The first set of pulleys 601 comprises a first pulley 705 and a secondpulley 706. Both the first pulley 705 and the second pulley 706 rotateabout the first axis 510. The first pulley 705 and the second pulley 706of the first set of pulleys are located on opposing sides of the firstjoint 506 in a longitudinal direction of the shaft 504. The first pulley705 and the second pulley 706 are located on opposing ends of the firstaxis 510. The first pulley 705 and the second pulley 706 are located onopposing sides of the first pair of driving elements A1,A2.

The second pair of driving elements B1,B2 is constrained to move aroundopposing sides of the first pulley 705 and the second pulley 706 of thefirst set of pulleys 601. The second pair of driving elements B1,B2 isconstrained to move around opposing sides of the first pulley 701 andthe second pulley 702 of the second set of pulleys 601. The second pairof driving elements is constrained to move around opposing sides of thefirst pulley 705 of the first set of pulleys 601 and the first pulley701 of the second set of pulleys 602. The second pair of drivingelements is constrained to move around opposing sides of the secondpulley 706 of the first set of pulleys 601 and the second pulley 702 ofthe second set of pulleys 602.

The third pair of driving elements C1,C2 is constrained to move aroundopposing sides of the first pulley 705 and the second pulley 706 of thefirst set of pulleys 601. The third pair of driving elements C1,C2 isconstrained to move around opposing sides of the first pulley 701 andthe second pulley 702 of the second set of pulleys 601. The third pairof driving elements is constrained to move around opposing sides of thefirst pulley 705 of the first set of pulleys 601 and the first pulley701 of the second set of pulleys 602. The third pair of driving elementsis constrained to move around opposing sides of the second pulley 706 ofthe first set of pulleys 601 and the second pulley 702 of the second setof pulleys 602.

The second and third pairs of driving elements are each constrained toextend over the first joint 506 in order to reach the second and thirdjoints respectively. Thus, the first one of the second pair of drivingelements B1 passes over one side of the first pulley 705 of the firstset of pulleys on the first joint axis 510, and the second one of thesecond pair of driving elements B2 passes over an opposing side of thesecond pulley 706 of the first set of pulleys on the first joint axis510, so that whatever rotation there is of the supporting body 509 aboutthe first joint 506, the length of the second pair of driving elementsB1,B2 is maintained the same. Similarly, the first one of the third pairof driving elements C1 passes over one side of the second pulley 706 ofthe first set of pulleys on the first joint axis 510, and the second oneof the third pair of driving elements C2 passes over an opposing side ofthe first pulley 705 of the first set of pulleys on the first joint axis510, so that whatever rotation there is of the supporting body 509 aboutthe first joint 506, the length of the third pair of driving elementsC1,C2 is maintained the same. If the arrangement of the instrumentinterface is symmetric for both the second pair of driving elementsB1,B2 and the third pair of driving elements C1,C2, then the length ofthe second pair of driving elements is the same as the length of thethird pair of driving elements for all rotation angles of the supportingbody 509 about the first joint 506. In every configuration of thesurgical instrument, the second pair of driving elements and the thirdpair of driving elements remain taut. They are never slack. Thus, thereis no backlash when articulating any of the joints of the surgicalinstrument. Thus, full control of all three degrees of freedom ofmovement of the surgical instrument is achieved in every configurationof the surgical instrument.

Suitably, each pulley of the first set of pulleys 601 comprises a pairof pulley elements. The first pulley 705 comprises an inside pulleyelement 708 and an outside pulley element 709. Inside pulley element 708is located between the outside pulley element 709 and the first pair ofdriving elements A1,A2. Suitably, inside pulley element 708 abutsoutside pulley element 709. The inside pulley element 708 may be fastwith the outside pulley element 709. The inside pulley element 708 maybe integrally formed with the outside pulley element 709. The secondpulley 706 comprises an inside pulley element 710 and an outside pulleyelement 711. Inside pulley element 710 is located between the outsidepulley element 711 and the first pair of driving element A1,A2.Suitably, inside pulley element 710 abuts outside pulley element 711.The inside pulley element 710 may be fast with the outside pulleyelement 711. The inside pulley element 710 may be integrally formed withthe outside pulley element 711. Each pulley element comprises a groovefor seating a driving element.

Suitably, each pulley of the second set of pulleys 602 comprises a pairof pulley elements. The first pulley 701 comprises an inside pulleyelement 712 and an outside pulley element 713. Inside pulley element 712is located between the outside pulley element 713 and the first pair ofdriving elements A1,A2. Suitably, inside pulley element 712 abutsoutside pulley element 713. The inside pulley element 712 may be fastwith the outside pulley element 713. The inside pulley element 712 maybe integrally formed with the outside pulley element 713. The secondpulley 702 comprises an inside pulley element 714 and an outside pulleyelement 715. Inside pulley element 714 is located between the outsidepulley element 715 and the first pair of driving element A1,A2.Suitably, inside pulley element 714 abuts outside pulley element 715.The inside pulley element 714 may be fast with the outside pulleyelement 715. The inside pulley element 714 may be integrally formed withthe outside pulley element 715. Each pulley element comprises a groovefor seating a driving element.

The second pair of driving elements B1,B2 is constrained to move aroundthe inside pulley element 712 of the first pulley of the second set ofpulleys and the outside pulley element 715 of the second pulley of thesecond set of pulleys. The second pair of driving elements B1, B2 isconstrained to move around the inside pulley element 708 of the firstpulley of the first set of pulleys and the outside pulley element 711 ofthe second pulley of the first set of pulleys.

The third pair of driving elements C1,C2 is constrained to move aroundthe outside pulley element 713 of the first pulley of the second set ofpulleys and the inside pulley element 714 of the second pulley of thesecond set of pulleys. The third pair of driving elements C1,C2 isconstrained to move around the outside pulley element 709 of the firstpulley of the first set of pulleys and the inside pulley element 710 ofthe second pulley of the first set of pulleys.

Thus, the second pair of driving elements B1,B2 has a symmetricallyopposing path around the first and second sets of pulleys 601, 602 thanthe third pair of driving elements C1,C2. In the straight configurationof the instrument in which the end effector is aligned with the shaft,the path of the second pair of driving elements B1,B2 about the pulleyarrangement is rotationally symmetrical about the longitudinal axis ofthe shaft 511 to the path of the third pair of driving elements C1,C2about the pulley arrangement. The second and third pairs of drivingelements B1,B2 and C1,C2 emerge from the second set of pulleys 602 intothe distal end of the shaft in a symmetrical arrangement. As can be moreeasily seen on FIGS. 7A-E, the driving elements B1 and C2 emergeadjacent to each other on one side of the shaft, and the drivingelements C1 and B2 emerge adjacent to each other on an opposing side ofthe shaft. The arrangement of driving elements B1 and C2 in the shaft isrotationally symmetrical to the arrangement of driving elements C1 andB2 in the shaft, about the longitudinal axis of the shaft 511. Thesecond set of pulleys 602 redirects the second and third pairs ofdriving elements from the first set of pulleys 601 into the shaft inthis manner.

FIGS. 7A-E illustrate the distal end of the surgical instrument in fivedifferent configurations. Configuration (c) is the straightconfiguration previously mentioned, in which the end effector is alignedwith the instrument shaft. In configurations (a), (b), (d) and (e),rotation about the first joint has occurred relative to configuration(c). In configurations (a), (b), (d) and (e), no rotation about eitherthe second or third joint has occurred relative to configuration (c).Starting from configuration (c), the driving element A2 (not shown) ispulled in order to cause the rotation about the first axis 510 leadingto the arrangement of configuration (b). The driving element A2 isfurther pulled to cause further rotation about the first axis 510 tolead to the arrangement of configuration (a). Starting fromconfiguration (c), the driving element A1 (not shown) is pulled in orderto cause rotation about the first axis 510 in an opposing direction tothat in configurations (a) and (b), thereby leading to the arrangementof configuration (d). The driving element A1 is further pulled to causefurther rotation about the first axis 510 to lead to the arrangement ofconfiguration (e).

Rotation of the end effector 501 about the first axis 510 is bounded bythe maximum travel of the first pair of driving elements A1,A2 about thefirst joint 506. Configuration (a) shows the end effector 501 at maximumrotation about the first axis 510 in one direction, and configuration(e) shows the end effector 501 at maximum rotation about the first axis510 in the opposing direction. The maximum rotation angle relative tothe longitudinal axis of the shaft 511 in both configurations is theangle φ. The second set of pulleys 602 are located relative to the firstset of pulleys 601 so as to ensure that the second and third pairs ofdriving elements are retained in contact with both the first set ofpulleys 601 and the second set of pulleys 602 even at the maximumrotation angle φ. For all rotation angles of the end effector 501 aboutthe first axis 510, the end effector 501 always lies within the conedefined by the tangential line connecting the first pulley 701 of thesecond set of pulleys and the first pulley 705 of the first set ofpulleys. That tangential line is the path taken by the driving element.The end effector 501 lies in this cone when the second and third jointsare retained in the straight configurations of FIGS. 5A and 5B, as shownin all the configurations of FIGS. 7A-E. As can be seen from FIGS. 7A-E,without the second set of pulleys 602, the driving elements B2 and C1would lose contact with the first set of pulleys 601 in configuration(a). Without the second set of pulleys 602, the driving elements B1 andC2 would lose contact with the first set of pulleys 601 in configuration(e).

The second and third pairs of driving elements are retained in contactwith the first and second sets of pulleys for all rotation angles of theend effector relative to the longitudinal axis of the shaft. Thus,regardless of the rotation about the first joint 506, the length of thesecond pair of driving elements B1,B2 will be maintained the same. Also,regardless of the rotation about the first joint 506, the length of thethird pair of driving elements C1,C2 will be maintained the same. Thus,the second set of pulleys enable tension to be retained in the secondand third driving elements regardless of how the first joint 506 isdriven about the first axis 510. Thus, control of the second and thirddriving elements is retained regardless of how the first joint 506 isdriven about the first axis 510.

The pulley arrangement further comprises a pair of redirecting pulleys716, 717. These redirecting pulleys are in the articulation 505 betweenthe first joint 506 and the second and third joints 507, 513. Theredirecting pulleys are positioned so as to redirect the second pair ofdriving elements B1,B2 from the first set of pulleys 601 to the secondjoint 507 and to redirect the third pair of driving elements C1,C2 fromthe first set of pulleys 601 to the third joint 513.

The second pair of driving elements B1,B2 is constrained to move aroundthe first redirecting pulley 716. The first redirecting pulley 716rotates about a first redirecting pulley axis 718. The first redirectingpulley axis 718 is at an angle θ to the first axis 510. The angle θ issuch that the first one of the second pair of driving elements B1 isredirected from a take-off point of the first pulley 705 of the firstset of pulleys 601 to a pick-up point 721 on the second joint 507.Suitably, the first redirecting pulley 716 comprises a groove whichseats the driving element B1. The third pair of driving elements C1,C2is not constrained to move around the first redirecting pulley 716.However, the second one of the third pair of driving elements C2 doespass by the first redirecting pulley 716 between its take-off point ofthe third joint 513 and its pick-up point on the first pulley 705 of thefirst set of pulleys 601. The driving element C2 may be partiallyenclosed by the first redirecting pulley 716. For example, the drivingelement C2 may partially pass between the wings of the groove of thefirst redirecting pulley 716, but the driving element C2 is not seatedin the groove of the first redirecting pulley 716.

The third pair of driving elements C1,C2 is constrained to move aroundthe second redirecting pulley 717. The second redirecting pulley 717rotates about a second redirecting pulley axis 719. The secondredirecting pulley axis 719 is at an angle ψ to the first axis 510. Theangle ψ is such that the first one of the third pair of driving elementsC1 is redirected from a take-off point 720 of the second pulley 706 ofthe first set of pulleys 601 to a pick-up point on the third joint 513.Suitably, the second redirecting pulley 717 comprises a groove whichseats the driving element C1. The second pair of driving elements B1,B2is not constrained to move around the second redirecting pulley 717.However, the second one of the second pair of driving elements B2 doespass by the second redirecting pulley 717 between its take-off point 720of the second joint 507 and its pick-up point on the second pulley 706of the first set of pulleys 601. The driving element B2 may be partiallyenclosed by the second redirecting pulley 717. For example, the drivingelement B2 may partially pass between the wings of the groove of thesecond redirecting pulley 717, but the driving element B2 is not seatedin the groove of the second redirecting pulley 717.

A take-off point is the point at which a driving element loses contactwith a pulley. A pick-up point is the point at which a driving elementfirst contacts a pulley. For a driving element passing directly from afirst pulley to a second pulley, the take-off point of the drivingelement from the first pulley and the pick-up point of the drivingelement on the second pulley are points on a line which is tangential toboth the first pulley and the second pulley, the take-off point beingwhere that tangential line intersects the first pulley, and the pick-uppoint being where that tangential line intersects the second pulley.This is for the purposes of explanation only and treats as negligiblethe thickness of the driving element. Thus, in reality, the tangentialline has a thickness equal to the thickness of the driving element, withthe take-off point being where one side of the tangential line meets thefirst pulley, and the pick-up point being where the other side of thetangential line meets the second pulley.

The redirecting pulley 716 causes the driving element B1 to wrap morefully around the second joint 507 than would happen if the redirectingpulley 716 was not there, thereby increasing the length of engagementbetween the driving element B1 and the second joint 507. Thus, thedriving element B1 has a greater travel around the second joint 507, andis hence able to cause a larger rotation of the end effector element 502about the second axis 512 than would be possible without the redirectingpulley 716. The redirecting pulley 716 causes the pick-up point of thedriving element B1 on the second joint 507 to change relative to whereit would have been without the redirecting pulley 716.

The redirecting pulley 717 causes the driving element C1 to wrap morefully around the third joint 513 than would happen if the redirectingpulley 717 was not there, thereby increasing the length of engagementbetween the driving element C1 and the third joint 513. Thus, thedriving element C1 has a greater travel around the third joint 513, andis hence able to cause a larger rotation of the end effector element 503about the second axis 512 than would be possible without the redirectingpulley 717. The redirecting pulley 717 causes the pick-up point of thedriving element C1 on the third joint 513 to change relative to where itwould have been without the redirecting pulley 717.

The redirecting pulleys are each located towards the outside edge of thearticulation, on opposing sides of the articulation. This is more easilyseen on FIG. 5A. As seen in FIG. 6A, each redirecting pulley is locatedbetween the longitudinal axis of the articulation and the externalprofile of the articulation, on opposing sides of the articulation.Suitably, the diameter of each redirecting pulley is maximised for thespace available. In other words, the redirecting pulley is as large aspossible, whilst enabling one driving element to engage the pulley onone side of the pulley and another driving element to pass next to thepulley on the opposing side of the pulley without snagging, the pulleyand the two driving elements being encapsulated within the profile ofthe articulation.

The first redirecting pulley 716 is located in a plane defined by thefollowing three points: (i) the desired take-off point of drivingelement B1 from the first pulley 705 of the first set of pulleys 601,(ii) the desired pick-up point of driving element B1 on the second joint507, and (iii) a point on the boundary of the articulation, the pointbeing such that the first redirecting pulley 716 is encapsulated withinthe boundary of the articulation when located in the plane. Suitably,the first redirecting pulley 716 is as large as possible whilst stillbeing located in this plane, encapsulated within the profile of thearticulation, not impeding the path of the driving element C2, andenabling driving element B1 to freely move around it.

The second redirecting pulley 717 is located in a plane defined by thefollowing three points: (i) the desired take-off point of drivingelement C1 from the second pulley 706 of the first set of pulleys 601,(ii) the desired pick-up point of driving element C1 on the third joint513, and (iii) a point on the boundary of the articulation, the pointbeing such that the second redirecting pulley 717 is encapsulated withinthe boundary of the articulation when located in the plane. Suitably,the second redirecting pulley 717 is as large as possible whilst stillbeing located in this plane, encapsulated within the profile of thearticulation, not impeding the path of the driving element B2, andenabling driving element C1 to freely move around it.

The desired take-off points and pick-up points are determined so as toallow the desired travel of the driving elements around the second andthird joints so as to allow the desired maximum rotation of the endeffector elements about the second axis.

The first and second redirecting pulleys are located in differentplanes. As can be seen in FIG. 6A, those planes may be symmetrical abouta plane which is perpendicular to the first axis 510. Those planes maybe rotationally symmetrical about a plane which is perpendicular to thefirst axis 510. Specifically, those planes may be rotationallysymmetrical about a line in a plane which is perpendicular to the firstaxis 510. When the instrument is in the straight configurationillustrated in FIG. 6A, those planes are rotationally symmetrical aboutthe longitudinal axis of the shaft 511. This is second order rotationalsymmetry. Those planes may be a reflection of each other in the planewhich is perpendicular to the first axis 510. In the exampleillustrated, the end effector elements 502 and 503 are rotationallysymmetrical, and the paths of the driving elements about the joints 507and 513 are rotationally symmetrical. Alternatively, the axes of the endeffector elements 502 and 503 may be rotationally asymmetrical and/orthe paths of the driving elements about the joints 507 and 513 may beasymmetrical. The paths of the driving elements about the joints 507 and513 may be asymmetrical as a result of the joints having differentdiameters (to enable different tension ratios) and/or being positionedat different offsets from the centreline of the supporting body 509. Inany of these alternative examples, the first and second redirectingpulleys 716 and 717 would not be rotationally symmetric. They would havedifferent sizes and/or different positions in order to cause the drivingelements to have the desired take-off points and pick-up points aspreviously described.

Suitably, the whole pulley arrangement comprising the first set ofpulleys, the second set of pulleys and the redirecting pulleys issymmetrical about a plane which is perpendicular to the first axis 510.Specifically, a first partial arrangement comprising the first pulley ofthe first set of pulleys 705, the first pulley of the second set ofpulleys 701, and the first redirecting pulley 716 is rotationallysymmetrical to a second partial arrangement comprising the second pulleyof the first set of pulleys 706, the second pulley of the second set ofpulleys 702, and the second redirecting pulley 717 about a plane whichis perpendicular to the first axis 510. Suitably, the first partialarrangement is a reflection of the second partial arrangement in thementioned plane which is perpendicular to the first axis 510. The secondpair of driving elements B1,B2 is constrained to move around the pulleyarrangement in a rotationally symmetrically opposing manner to that inwhich the third pair of driving elements C1,C2 is constrained to movearound the pulley arrangement. Since the pulley arrangement has thedescribed symmetry, the second and third driving elements that areconstrained to move symmetrically around the pulley arrangement alsohave the same symmetry. Thus, the path of the second pair of drivingelements B1,B2 about the pulley arrangement is rotationally symmetricalto the path of the third pair of driving elements C1,C2 about the pulleyarrangement.

In an exemplary implementation, the first and second redirecting pulleysare mounted on the supporting body 509. FIG. 10 illustrates thesupporting body 509 and the redirecting pulleys in isolation. Eachredirecting pulley is mounted to a surface of the supporting body 509 bya spindle. The spindle 1001 secures the first redirecting pulley 716 tothe supporting body 509. A spindle 1102 also secures the secondredirecting pulley 717 to the supporting body 509.

As is more clearly illustrated in the view shown in FIGS. 11A and 11B,the supporting body 509 has a bevelled surface 1101 onto which the firstredirecting pulley 716 is mounted. The first redirecting pulley 716 hasa mounting surface 1104 which faces the bevelled surface 1101 of thesupporting body 509. The mounting surface 1104 is flush with thebevelled surface 1101. The first redirecting pulley has an opposingsurface 1105 which opposes the mounting surface 1104. The opposingsurface 1105 is parallel to the mounting surface 1104. The supportingbody 509 has a further bevelled surface onto which the secondredirecting pulley 717 is mounted by spindle 1103. The secondredirecting pulley 717 has a mounting surface 1106 which faces thebevelled surface 1102 of the supporting body 509. The mounting surface1106 is flush with the bevelled surface 1102. The second redirectingpulley has an opposing surface 1107 which opposes the mounting surface1102. The opposing surface 1107 is parallel to the mounting surface1102.

The bevelled surfaces of the supporting body 509 are not parallel to thelongitudinal axis of the supporting body. The bevelled surface 1101 ofthe supporting body 509 is located in a plane 1108 parallel to the plane1109 in which the first redirecting pulley 716 is located. In otherwords, the bevelled surface 1101 is located in a plane 1108 parallel tothe plane 1109 defined by the following three points: (i) the desiredtake-off point of driving element B1 from the first pulley 705 of thefirst set of pulleys 601, (ii) the desired pick-up point of drivingelement B1 on the second joint 507, and (iii) a point on the boundary ofthe articulation, the point being such that the first redirecting pulley716 is encapsulated within the boundary of the articulation when locatedin the plane 1109. The plane 1108 of the bevelled surface 1101 is offsetfrom the plane 1109 defined by these points by half the width of thefirst redirecting pulley 716, illustrated as d₁ in FIGS. 11A and 11B.

The bevelled surface 1102 of the supporting body 509 is located in aplane 1110 parallel to the plane 1111 in which the second redirectingpulley 717 is located. In other words, the bevelled surface 1102 islocated in a plane 1110 parallel to the plane 1111 defined by thefollowing three points: (i) the desired take-off point of drivingelement C1 from the second pulley 706 of the first set of pulleys 601,(ii) the desired pick-up point of driving element C1 on the third joint513, and (iii) a point on the boundary of the articulation, the pointbeing such that the second redirecting pulley 717 is encapsulated withinthe boundary of the articulation when located in the plane 1111. Theplane 1110 of the bevelled surface 1101 is offset from the plane 1111defined by these points by half the width of the second redirectingpulley 717, illustrated as d₂ in FIGS. 11A and 11B. Suitably, the firstredirecting pulley 716 and the second redirecting pulley 717 are thesame shape and size. In this case, d₁=d₂.

As discussed above, each redirecting pulley is mounted to thecorresponding bevelled surface of the supporting body by a spindle. Thespindle comprises a spindle body and a spindle head. The spindle bodypasses through a central aperture of the redirecting pulley. The centralaperture is a through-hole which extends perpendicularly between themounting surface and the opposing surface of the redirecting pulley. Thespindle body passes through the central aperture of the redirectingpulley into a bore of the supporting body. FIGS. 12 and 13 illustratethe supporting body 509 in isolation. An exemplary implementation of thebore of the supporting body is depicted in these figures. The bore is arecess in the supporting body which tapers to a point. The spindle bodypasses through the initial opening of the bore and securely lodges inthe tapered section. The spindle head is bigger than the centralaperture of the redirecting pulley, and thus is unable to pass throughthe central aperture of the redirecting pulley. Consequently, thespindle head secures the redirecting pulley flush against the bevelledsurface of the supporting body. The spindle head contacts at least aportion of the opposing surface of the redirecting pulley, through whichcontact the redirecting pulley is retained against the bevelled surface.

Referring to FIG. 14, the diameter of the bore 1401 through thesupporting body is greater than the diameter of the spindle body 1403.The diameter of the central aperture 1402 of the redirecting pulley maybe greater than the diameter of the spindle body 1403. Thus, the spindlebody may loosely fit through the central aperture of the redirectingpulley. The spindle body loosely fits through the bore of the supportingbody except for in the region in which it is secured to the bore, in theexample above the tapered section. Typically, the bore through thesupporting body is created by drilling through the bevelled surface ofthe supporting body during manufacture. Since the opening of the bore inthe bevelled surface has a greater diameter than the spindle body, theprecision of the angle at which the supporting body is drilled to createthe bore is not critical. The spindle sits in the bore at the correctangle for the redirecting pulley to sit flush with the bevelled surface.It would have been critical that the angle of the bore was drilled veryaccurately if the fit of the spindle body through the bore was a tightfit and was the means by which the redirecting pulley was caused torotate about the redirecting pulley axis 718,719. In that case thepulley would have been mounted tight on to the spindle which would havebeen mounted tight into the bore to stop the pulley from precessing.Thus, there would have been no room for manufacturing deviations in theangle at which the hole was drilled through the supporting body. In thedescribed implementation, however, the redirecting pulley is caused torotate about the redirecting pulley axis 718,719 as a result of theredirecting pulley being held flush against a bevelled surface of thesupporting body 509 which is perpendicular to the redirecting pulleyaxis 718,719. Thus, greater manufacturing variation in the accuracy ofthe angle at which the bore is drilled through the supporting body isacceptable in the described implementation.

The bevelled surfaces 1101 and 1102 of the supporting body are notparallel to each other. The bevelled surfaces may be symmetrical about aplane which is perpendicular to the first axis 510. The bevelledsurfaces may be rotationally symmetrical about a plane which isperpendicular to the first axis 510. Specifically, the bevelled surfacesmay be rotationally symmetrical about a line in a plane which isperpendicular to the first axis 510. When the instrument is in thestraight configuration illustrated in FIG. 5a , the bevelled surfacesare rotationally symmetrical about the longitudinal axis of the shaft511. This is second order rotational symmetry. The bevelled surfaces maybe a reflection of each other in the plane which is perpendicular to thefirst axis 510.

Referring to FIG. 15, in one example, the supporting body 509 comprisesgrooves adjacent to each bevelled surface for seating a driving element.The supporting body comprises a groove 1501 adjacent the bevelledsurface 1101 for seating the second one C2 of the third pair of drivingelements. The driving element C2 is seated in the groove 1501 andpartially enclosed by the first redirecting pulley 716. The supportingbody comprises a groove 1502 adjacent the bevelled surface 1102 forseating the second one B2 of the second pair of driving elements. Groove1502 is shown in FIGS. 11A and 11B. The driving element B2 is seated inthe groove 1502 and partially enclosed by the second redirecting pulley717.

The first, second and third pairs of driving elements extend through theinstrument shaft from the distal end of the shaft connected to thearticulation to the proximal end of the shaft connected to a drivemechanism of the instrument interface. FIGS. 17A and 17B illustrate twoviews of the first, second and third pairs of driving elements extendingfrom the described articulation to an exemplary instrument interface1701. In an exemplary implementation, the second and third pairs ofdriving elements overlap in the shaft so as to emerge from the proximalend of the shaft in a different arrangement to that at which they are inat the distal end of the shaft. FIGS. 16A and 16B illustratecross-sections of the shaft depicting the positions of the drivingelements.

Configuration (a) of FIGS. 16A and 16B show a cross-section of the shaftat the distal end of the shaft. In other words, configuration (a) showsthe positions of the driving elements just as they have left the secondset of pulleys 602. The driving elements A1 and A2 are at opposing sidesof the shaft after having left the first joint 506. The driving elementsC1 and B2 are adjacent each other on an opposing side of the shaft tothe driving elements B1 and C2 which are also adjacent each other. Thedriving elements C1 and B2 are offset from the driving elements B1 andC2 about an axis 1601 which is transverse to the axis 1602 connectingdriving elements A1 and A2. This is a result of the offset axes of thetwo pulleys of the second set of pulleys.

Configuration (b) of FIGS. 16A and 16B shows a cross-section of theshaft at the proximal end of the shaft. In other words, configuration(b) shows the positions of the driving elements as they are about toexit the shaft into the instrument interface. The first pair of drivingelements A1 and A2 are on opposing sides of the shaft in a similararrangement to their arrangement in configuration (a). The first pair ofdriving elements may be closer together, by virtue of them having movedslightly towards each other over the course of their extent through theshaft. In configuration (b), driving element B1 is located on anopposing side of the shaft to its location in configuration (a). Inconfiguration (b), driving element C1 is located on an opposing side ofthe shaft to its location in configuration (a). To achieve this, drivingelement B1 and driving element C1 have not extended down the shaftparallel to the longitudinal axis of the shaft 511. Instead, drivingelement B1 and driving element C1 have overlapped each other duringtheir extent in the shaft. This overlapping occurs without the drivingelements B1 and C1 clashing because of their offset positions inconfiguration (a) owing to the pulleys of the second set of pulleys 602having offset axes. Driving element B2 has moved a little in the shaft,but remained on the same side of the shaft as in configuration (a), soas to emerge at the proximal end of the shaft adjacent to drivingelement B1. Driving element C2 has moved a little in the shaft, butremained on the same side of the shaft as in configuration (a), so as toemerge at the proximal end of the shaft adjacent to driving element C1.

The instrument interface comprises a further pulley arrangement aroundwhich the first, second and third pairs of driving elements areconstrained to move. The driving elements A1, A2, B1, B2, C1 and C2emerge at the proximal end of the shaft in a configuration which enablesthem to engage directly with components of the instrument interface. Inone implementation, the driving elements emerge at the proximal end ofthe shaft as shown in configuration (b) in order to engage directly withthe further pulley arrangement of the instrument interface describedherein. Suitably, the first, second and third driving elements extendfrom the pulley arrangement at the distal end of the shaft to theinstrument interface without wrapping around any intervening pulleys.Suitably, there are no intervening pulleys in the shaft around which thefirst, second and/or third pairs of driving elements are constrained tomove.

As can be seen in FIGS. 17A and 17B, the instrument interface isrelatively flat. The instrument interface extends mostly in a centralplane viewed head on in FIG. 17A. Suitably, the instrument shaft 504 isrigidly attached to the instrument interface 1701. The instrument shaft504 does not rotate or otherwise move relative to the instrumentinterface 1701. Suitably, the second axis 512 about which the endeffector elements 502, 503 rotate is perpendicular to the central planeof the instrument interface. This is the case in the straightconfiguration of the instrument shown in FIGS. 17A and 17B. Thus, in thestraight configuration of the instrument, the jaws of the end effectorare moveable in the central plane of the instrument interface.

A driving element may be a uniform component having the same shape andsize along its length and constructed of the same material along itslength. Alternatively, the driving element may be composed of differentportions. In one example, the portion of the driving element whichengages components of the instrument interface (such as pulleys andinterface elements) is flexible. Similarly, the portion of the drivingelement which engages components of the distal end of the surgicalinstrument (such as the pulleys and joints in the articulation) isflexible. Between these two flexible portions are spokes 1702illustrated in FIGS. 17A and 17B. Thus, each pair of driving elementscomprises two spokes and two flexible portions. Each pair of drivingelements forms a loop. The loop comprises alternating spokes andflexible portions. The two spokes are predominantly or wholly enclosedin the instrument shaft. A distal flexible portion terminates at one endin the distal end of one of the spokes, and at the other end in thedistal end of the other spoke. The distal flexible portion engagescomponents of the articulation. A proximal flexible portion terminatesat one end in the proximal end of one of the spokes, and at the otherend in the proximal end of the other spoke. The proximal flexibleportion engages components of the instrument interface. The spokes arestiffer than the flexible portions. Suitably, the spokes are rigid. Thespokes may be hollow. Typically, the spokes have a larger diameter thanthe flexible portions. Thus, the flexible portions may be cables, andthe spokes hollow tubes. The flexible portions may terminate where theymeet the spokes. Alternatively, the spokes may encapsulate the materialof the flexible portions. For example, the spokes may be rigid sheathswhich cover flexible cables.

The spokes are stiffer than the flexible portions. Thus, by forming apair of driving elements from spokes as well as flexible portions, thelikelihood of the driving element stretching is reduced. For thisreason, the proportion of each driving element which is a spoke ispreferably maximised whilst ensuring that the spoke does not come intocontact with components of the articulation or the instrument interface,and also that adjacent driving elements do not collide. The spokes arestronger than the flexible portions, and hence more resilient tocompression and tension forces applied in any direction than theflexible portions. Thus, by incorporating the spokes, the drivingelement as a whole is stiffer and less likely to stretch. Thus, thelifetime of the driving element before it needs re-tensioning orreplacing is extended.

In FIG. 18 the spokes of the driving elements A1, A2, B1 and C1 arevisible, labelled as A1 s, A2 s, B1 s and C1 s respectively. FIG. 18depicts a straight configuration of the surgical instrument in which theend effector 501 is aligned with the shaft 504. As can be seen in FIG.18, the distal flexible portion of driving element A1 terminates in thespoke A1 s at a point 1801 along the longitudinal direction x of theshaft. The longitudinal direction x is the direction of the longitudinalaxis 511 of the shaft. The distal flexible portion of driving element A2terminates in the spoke A2 s at a point 1802 along the longitudinaldirection x of the shaft. The distal flexible portion of driving elementB1 terminates in the spoke B1 s at a point 1803 along the longitudinaldirection x of the shaft. The distal flexible portion of driving elementC1 terminates in the spoke C1 s at a point 1804 along the longitudinaldirection x of the shaft. The distal flexible portions of drivingelements B2 and C2 terminate in their respective spokes further towardsthe proximal end of the shaft, as can be seen in FIG. 17A.

As can be seen in FIG. 18, the longitudinal positions 1801, 1802, 1803and 1804 at which the distal flexible portions of the driving elementsterminate in the distal ends of the spokes are not coincident when theinstrument is in the straight configuration depicted. Instead, thelongitudinal positions 1801, 1802, 1803 and 1804 are offset from eachother. In other words, the distal ends of the spokes of the drivingelements are offset along the longitudinal direction of the shaft whenthe instrument is in the straight configuration. Specifically, thedistal ends of adjacent spokes are offset along the longitudinaldirection of the shaft in the straight configuration. The distal ends ofspokes which are not adjacent to each other may be coincident along thelongitudinal direction of the shaft in the straight configuration. Forexample, in FIG. 18, the non-adjacent spokes A1 s and A2 s bothterminate at the same point 1801,1802 along the longitudinal directionof the shaft. Suitably, the distal ends of the spokes of the drivingelements are offset along the longitudinal direction of the shaft inevery configuration of the surgical instrument. Specifically, suitably,the distal ends of adjacent spokes are offset along the longitudinaldirection of the shaft in every configuration of the surgicalinstrument.

As previously discussed in relation to FIGS. 16A and 16B, the drivingelements do not all extend parallel to each other in the shaft in animplementation in which driving elements pass directly from the pulleyarrangement at the distal end of the shaft to the pulley arrangement inthe instrument interface without moving around any intervening pulleys.The first one of the first pair of driving elements A1 extendssubstantially parallel to the second one of the first pair of drivingelements A2 in the shaft. Driving elements A1 and A2 may move slightlycloser to each other over the course of the length of the shaft in thedirection from the articulation to the instrument interface. The firstone of the second pair of driving elements B1 extends at an angle to thesecond one of the second pair of driving elements B2 in the shaft.Driving element B1 also extends at an angle to driving elements A1, A2,C1 and C2 down the shaft. Driving element B2 extends at an angle todriving elements A1, A2, C1 and C2 down the shaft. The first one of thethird pair of driving elements C1 extends at an angle to the second oneof the third pair of driving elements C2 in the shaft. Driving elementC1 also extends at an angle to driving elements A1, A2, B1 and B2 downthe shaft. Driving element C2 extends at an angle to driving elementsA1, A2, B1 and B2 down the shaft.

The longitudinal positions of the distal ends of the spokes are selectedsuch that the spokes do not collide when the instrument is beingarticulated. Since the spokes have a larger diameter than the flexibleportions, although the flexible portions can extend down the length ofthe shaft without colliding the spokes may not be able to. Suitably, thelongitudinal positions of the distal ends of the spokes in the straightconfiguration of the instrument are such that for any configuration ofthe end effector, no portion of any driving element contacts a portionof another driving element. Suitably, the positions of the proximal anddistal ends of the spokes in the straight configuration are selected soas to maximise the spoke length whilst satisfying the condition that thedriving elements will not contact. The spokes are stiffer than theflexible portions. Thus, this maximises the stiffness of the drivingelements whilst enabling them to wrap around components in thearticulation and instrument interface. This maximises the strength ofthe driving elements whilst enabling them to wrap around components inthe articulation and instrument interface.

In FIG. 19A the spokes of the driving elements A1, A2, B1 and C1 arevisible, labelled as A1 s, A2 s, B1 s and C1 s respectively. FIG. 19Adepicts a non-straight configuration of the surgical instrument in whichthe end effector 501 is not aligned with the shaft 504. As can be seenin FIG. 19A, the proximal flexible portion of driving element A1terminates in the spoke A1 s at a point 1901 along the longitudinaldirection x of the shaft. The longitudinal direction x is the directionof the longitudinal axis 511 of the shaft. The proximal flexible portionof driving element A2 terminates in the spoke A2 s at a point 1904 alongthe longitudinal direction x of the shaft. The proximal flexible portionof driving element B1 terminates in the spoke B1 s at a point 1902 alongthe longitudinal direction x of the shaft. The proximal flexible portionof driving element C1 terminates in the spoke C1 s at a point 1903 alongthe longitudinal direction x of the shaft. The proximal flexibleportions of driving elements B2 and C2 terminate in their respectivespokes further towards the distal end of the shaft, as can be seen inFIG. 17A. The spokes may terminate in the proximal flexible portionsinside the shaft, as is the case in the example shown for drivingelements B2 and C2. The spokes may terminate in the proximal flexibleportions inside the instrument interface, as is the case in the exampleshown for driving elements A1, A2, B1 and C1. Some spokes may terminatein the proximal flexible portions inside the shaft and some spokes mayterminate in the proximal flexible portions inside the instrumentinterface. In the design of the instrument interface depicted in FIG.19A, the driving elements B2 and C2 engage pulleys as they enter theinstrument interface from the shaft, thus the spokes of driving elementsB2 and C2 terminated in their proximal flexible portions in the shaft(not shown) to enable the proximal flexible portions to engage thepulleys. Driving elements A1, A2, B1 and C1 all extend some distanceinto the instrument interface before engaging with components of theinstrument interface, thus the spokes of driving elements A1, A2, B1 andC1 are able to extend into the instrument interface.

As can be seen in FIG. 19A, the longitudinal positions 1901, 1902, 1903and 1904 at which the proximal flexible portions of the driving elementsterminate in the proximal ends of the spokes are not coincident.Instead, the longitudinal positions 1901, 1902, 1903 and 1904 are offsetfrom each other. In other words, the proximal ends of the spokes of thedriving elements are offset along the longitudinal direction of theshaft when the instrument is in the configuration shown. Suitably, theproximal ends of the spokes of the driving elements are offset along thelongitudinal direction of the shaft for the straight configuration ofthe instrument. Specifically, the proximal ends of adjacent spokes areoffset along the longitudinal direction of the shaft in the straightconfiguration. The proximal ends of spokes which are not adjacent toeach other may be coincident along the longitudinal direction of theshaft in the straight configuration. For example, in FIG. 19A, thenon-adjacent spokes B1 s and C1 s both terminate at the same point1902,1903 along the longitudinal direction of the shaft. Suitably, theproximal ends of the spokes of the driving elements are offset along thelongitudinal direction of the shaft in every configuration of thesurgical instrument. Specifically, suitably, the distal ends of adjacentspokes are offset along the longitudinal direction of the shaft in everyconfiguration of the surgical instrument.

The longitudinal positions of the proximal ends of the spokes areselected such that the spokes do not collide when the instrument isbeing articulated. Suitably, the longitudinal positions of the proximalends of the spokes in the straight configuration of the instrument aresuch that for any configuration of the end effector, no portion of anydriving element contacts a portion of another driving element.

Each pair of driving elements engages a single instrument interfaceelement in the instrument interface. Each driving element engages aninstrument interface element in the instrument interface. In the exampleillustrated in FIGS. 19A, 19B and 19C, each driving element engages itsown instrument interface elements. A single instrument interface elementdrives a pair of driving elements. Each driving element is drivenindependently by a single instrument interface. In alternativearrangements, there may be a compound driving motion in which more thanone instrument interface element drives a single driving element, asingle instrument interface element drives more than one pair of drivingelements, or a plurality of instrument interface elements collectivelydrive a plurality of driving elements.

FIG. 19B illustrates a first instrument interface element 1905 whichengages the first pair of driving elements A1,A2. A second instrumentinterface element 1906 engages the second pair of driving elementsB1,B2. A third instrument interface element 1907 engages the third pairof driving elements C1,C2. Suitably, each driving element is secured toits associated instrument interface element. In other words, eachdriving element is fast with its associated instrument interfaceelement.

The instrument interface 1701 has a significantly larger profile thanthe instrument shaft 504. Typically, the instrument shaft has a circularcross-section having a diameter of less than or the same as 5 mm,whereas a corresponding cross-section through the instrument interfacemay be larger than this. The instrument interface comprises an internalportion and an external portion. The internal portion is bounded by thedotted line 1950 (shown in FIGS. 19A and 19B). The external portion isthe remainder of the instrument interface which is not in the internalportion. The internal portion is within the projected profile of theshaft. In other words, the internal portion is the part of theinstrument interface that would have been encompassed had the profile ofthe shaft continued within the instrument interface. The externalportion is outside of the projected profile of the shaft. In the exampleillustrated, the shaft has a constant circular cross-section, and hencethe internal portion is a cylinder having the same circularcross-section as the shaft, and having the same longitudinal axis 511 asthe shaft. In other words, the internal portion is an extrapolation ofthe constant cross-section of the shaft in the instrument interface. Theinternal portion 1950 is shown from the side in FIG. 19A and from thetop in FIG. 19B.

The instrument interface elements 1905, 1906 and 1907 are dispersedacross the width of the instrument interface as shown in FIG. 19B. Inthe arrangement depicted in FIG. 19B, one instrument interface element1905 is within the internal portion 1950 of the instrument interface.Specifically, the part of the instrument interface element 1905 whichengages the driving element is within the internal portion 1950 of theinstrument interface. The instrument interface element 1905 as a wholemay be substantially within the internal portion 1950 of the instrumentinterface, as shown in FIG. 19B. The instrument interface element 1905as a whole may be wholly within the internal portion 1950 of theinstrument interface. Suitably, the instrument interface element 1905 isaligned with the longitudinal axis 511 of the shaft 504. In an exemplaryarrangement, only one instrument interface element is located within theinternal portion of the instrument interface. The remainder of theinstrument interface elements 1906, 1907 are within the external portionof the instrument interface. These other instrument interface elements1906, 1907 are located on either side of the aligned instrumentinterface element 1905. Specifically, the other instrument interfaceelements 1906, 1907 are located on either side of the aligned instrumentinterface element 1905 in a direction perpendicular to the longitudinalaxis of the shaft 511. The instrument interface elements 1906 and 1907are not aligned with the longitudinal axis 511 of the shaft 504. Theinstrument interface elements 1906 and 1907 are constrained to moveparallel to the longitudinal axis 511 of the shaft 504, since they areconstrained to move along rails 1929 and 1930 respectively.

Instrument interface element 1905 engages a first pair of drivingelements A1, A2. As can be seen in FIG. 19A, between the proximal end ofthe shaft and the instrument interface element 1905, the pair of drivingelements A1, A2 lie wholly within the internal portion 1950. Between theproximal end of the shaft and the instrument interface element 1905, thepair of driving elements A1, A2 lie wholly parallel to the longitudinalaxis of the shaft 511. Suitably, there are no intervening pulleys orother structures in the instrument interface around which the pair ofdriving elements A1, A2 is constrained to move between the proximal endof the shaft and the instrument interface element 1905. Suitably, onlyinstrument interface element 1905 engages its pair of driving elementsA1, A2 in the internal portion 1950 of the instrument interface.

Instrument interface element 1906 engages a second pair of drivingelements B1, B2. The instrument interface element 1906 engages thesecond pair of driving elements B1, B2 in the external portion of theinstrument interface.

Instrument interface element 1907 engages a third pair of drivingelements C1, C2. The instrument interface element 1907 engages the thirdpair of driving elements C1, C2 in the external portion of theinstrument interface.

A pulley arrangement is used to shift the driving elements over toengage with the instrument interface elements which are in the externalportion. Each pair of driving elements engages a first pair of pulleysto shift it over from the proximal end of the shaft 504 to itsrespective instrument interface element, and a second pair of pulleys toshift it back from alignment with the instrument interface element toalignment with the shaft 504.

In the arrangement shown, the second pair of driving elements B1,B2emerges from the proximal end of the shaft in a direction aligned withthe shaft. The driving elements B1,B2 do not run exactly parallel to thelongitudinal axis 511 of the shaft 504 as a result of the directionchanges described with respect to FIGS. 16A and 16B. The second pair ofdriving elements B1, B2 is then constrained to move around pulley pair1908 and 1909 to shift it from where it emerges from the shaft 504 toengagement with the second instrument interface element 1906. The secondpair of driving elements B1, B2 emerges from the pulley pair 1908 and1909 in a direction parallel to and offset from the direction that thesecond pair of driving elements B1, B2 emerges from the proximal end ofthe shaft. The second pair of driving elements B1,B2 is constrained tomove around pulley pair 1910 and 1911 to shift it from alignment withthe second instrument interface element 1906 to alignment with the shaft504.

In the arrangement shown, the third pair of driving elements C1, C2emerges from the proximal end of the shaft in a direction aligned withthe shaft. The driving elements C1,C2 do not run exactly parallel to thelongitudinal axis 511 of the shaft 504 as a result of the directionchanges described with respect to FIGS. 16A and 16B. The third pair ofdriving elements C1,C2 is then constrained to move around pulley pair1912 and 1913 to shift it from where it emerges from the shaft 504 toengagement with the third instrument interface element 1907. The thirdpair of driving elements C1, C2 emerges from the pulley pair 1912 and1913 in a direction parallel to and offset from the direction that thethird pair of driving elements C1, C2 emerges from the proximal end ofthe shaft. The third pair of driving elements C1,C2 is constrained tomove around pulley pair 1914 and 1915 to shift it from alignment withthe third instrument interface element 1907 to alignment with the shaft504.

In the arrangement shown in FIGS. 19A, 19B and 19C, pair of drivingelements A1, A2 engage with the first instrument interface element 1905which is within the internal portion. Pair of driving elements A1, A2drive rotation of the articulation, and hence the end effector, aboutthe first axis 510 (see FIG. 5A). There is a smaller range of motionabout first joint 506 than there is about second joint 507 and thirdjoint 513. As described below, the first instrument interface element1905 is linearly displaceable through a maximum distance d₁ minus thelength of the first instrument interface element 1905, which is smallerthan the maximum displacement of the second instrument interface element1906 d₂ minus the length of the second instrument interface element1906, and smaller than the maximum displacement of the third instrumentinterface element 1907 d₃ minus the length of the third instrumentinterface element 1907. Since motion about the first joint 506 iscontrolled via a shorter range of travel of the instrument interfaceelement than the second and third joints, greater sensitivity of thatmotion is preferred. Cables may slip and/or stretch over pulleys. Thus,the simplest cabling scheme is preferably utilised for transferringmotion between the first instrument interface element and the firstjoint 506.

By locating the first instrument interface element 1905 within theinternal portion on the longitudinal axis of the shaft 511, the firstpair of driving elements is not constrained to pass around anyintervening pulleys between the first joint 506 and the first instrumentinterface element 1905.

Each instrument interface element is displaceable within the instrumentinterface. Since each instrument interface element is secured to acorresponding pair of driving elements, a displacement of the instrumentinterface element is transferred to a displacement of the pair ofdriving elements. Suitably, each instrument interface element isdisplaceable along the same line as the line of the pair of drivingelements that it is secured to. Each instrument interface elementengages with a corresponding drive assembly interface element of therobot arm. Thus, displacement of the instrument interface element isdriven by the robot arm. In this way, the robot arm drives the pairs ofdriving elements.

Each pair of driving elements engages with an instrument interfaceelement in the instrument interface. The pair of driving elements alsoengages with a tensioning mechanism and an alignment mechanism. Whenmanufacturing the instrument, the tensioning mechanism is used toachieve a desired tension in the pair of driving elements. The alignmentmechanism is used to set the instrument interface elements to apredetermined alignment position in the longitudinal direction of theshaft when the end effector has a predetermined configuration. Eachinstrument interface element has a displacement range over which it isdisplaceable. The predetermined alignment position may be the midpointof the displacement range for each instrument interface element. Thepredetermined configuration of the end effector may be the straightconfiguration, in which the end effector elements are closed together(for example the jaws are closed), and the longitudinal axis of thearticulation and the longitudinal axis of the end effector are alignedwith the longitudinal axis of the shaft 511. By setting the instrumentinterface elements to a predetermined alignment position when the endeffector has a predetermined configuration, when changing instrumentsduring an operation, the time taken to set up the new instrument readyfor use may be reduced. In practice, when an instrument is removed fromthe robot arm, the robot arm assembly may be configured to go to anarrangement in which it is ready to receive the instrument interfaceelements in the predetermined alignment position. For example, the robotarm assembly interface elements may go to a default position in whichthey are arranged to receive each of the instrument interface elementsat the midpoint of their displacement range. Then, the instrument ismanually put in the predetermined configuration and then slotted intothe robot arm. For example, the technician moves the articulation andend effector into the straight configuration and then slots theinstrument into the robot arm. Because it is known that the instrumentinterface elements have the predetermined alignment position when theinstrument is in the predetermined configuration, the instrumentinterface elements engage directly with the robot arm assembly interfaceelements. The control system does not need to perform an additionalcalibration or software setup procedure in order to map the position andorientation of the end effector, because it is known that the endeffector is in the predetermined configuration.

The following describes tensioning and alignment mechanisms which areindependent of each other. By isolating the tensioning mechanism fromthe alignment mechanism the process by which the desired tension anddesired alignment are achieved is simplified. Thus, the time taken toachieve the desired tension and desired alignment during manufacture isreduced.

FIGS. 19A, 19B and 19C illustrate a tensioning mechanism utilisingpulleys. Each pair of driving elements is independently tensioned. Eachpair of driving elements is constrained to move around a pulley which isdisplaceable. FIGS. 19A, 19B and 19C depict two different exemplarypulley arrangements for tensioning the pairs of driving elements. Inboth examples, the pulley is linearly displaceable.

Referring firstly to the tensioning mechanism shown for the pairs ofdriving elements B1,B2 and C1,C2. Taking pair of driving elements B1,B2first, pulley 1911 is used to tension B1,B2. Pulley 1911 is linearlydisplaceable along a displacement axis 1920 which is parallel to thelongitudinal axis 511 of the shaft. The displacement axis 1920 is offsetfrom the longitudinal axis 511 of the shaft. Displacement axis 1920 isshown in FIG. 19B. The tensioning pulley 1911 is mounted to a block 1918which is slideable along a rail 1919. Sliding the block 1918 along therail 1919 causes the pulley 1911 to displace along the displacement axis1920. When the block 1918 is moved away from the shaft, the tension ofthe second pair of driving elements B1,B2 increases. When the block 1918is moved towards the shaft, the tension of the second pair of drivingelements B1,B2 decreases. Any suitable mechanism may be used to move theblock. For example, a screw adjustment mechanism may be used. FIGS. 19A,19B and 19C show a screw adjustment mechanism in which screw 1921 isthreaded into block 1918. This is most clearly seen on FIG. 19A. Thescrew 1921 is constrained by portion 1922 of the instrument interfacesuch that it is able to rotate but not able to be displaced linearly.Thus, when the screw is rotated, the screw thread engages with thethread inside the block 1918 causing the block and hence the pulley 1911to displace linearly. When the screw 1921 is tightened, the pulley 1911moves in one linear direction. When the screw 1921 is loosened, thepulley 1911 moves in the opposing linear direction. The tensioningmechanism for driving elements C1,C2 depicted in FIGS. 19A, 19B and 19Cworks in a corresponding manner to that described with relation todriving elements B1,B2.

Referring now to the tensioning mechanism shown for the first pair ofdriving elements A1,A2 in FIG. 19A. Pulley 1923 is used to tensionA1,A2. Pulley 1923 is linearly displaceable along a displacement axis1924. Displacement axis 1924 is at an angle to the longitudinal axis 511of the shaft. Suitably, the displacement axis 1924 may be at a 45° angleto the longitudinal axis 511 of the shaft. The tensioning pulley 1923 ismounted to a block 1925 which is captive in a socket 1926 of theinstrument interface. The block 1925 and tensioning pulley 1923 are ableto slide through the socket 1926. Sliding the block 1925 through thesocket 1926 causes the pulley to displace along the displacement axis1924. When the block 1925 is slid further into the socket, the tensionof the first pair of driving elements A1,A2 increases. When the block1925 is slid out of the socket, the tension of the first pair of drivingelements A1,A2 decreases. Any suitable mechanism may be used to move theblock 1925. For example, a screw adjustment mechanism as described abovewith respect to block 1918 may be used. Since the first pair of drivingelements A1,A2 wrap almost fully around tensioning pulley 1923 such thatthey run almost parallel to each other, a greater tension is applied perunit displacement of the tensioning pulley compared to the tensioningmechanism described with respect to the second and third pairs ofdriving elements.

Although FIGS. 19A, 19B and 19C show the first pair of driving elementsusing the angled tensioning mechanism, and the second and third pairs ofdriving elements using the linear tensioning mechanism, any pair ofdriving elements may be tensioned using any suitable mechanism as longas that mechanism packages into the instrument interface.

FIG. 20A illustrates an alternative tensioning mechanism. Each pair ofdriving elements terminates in a lug 1927 of an instrument interfaceelement (see FIG. 19C). FIG. 20A illustrates an alternative arrangementof lug 1927 to that shown in FIG. 19C. In the arrangement of FIG. 20A,the lug is utilised in the tensioning mechanism. The lug of FIG. 20A hasa pair of lug elements 2001 and 2002. One driving element of a pair ofdriving elements terminates in one lug element, and the other drivingelement of the pair of driving elements terminates in the other lugelement. A first one of the third pair of driving elements C1 has beendepicted as terminating in lug element 2001, and the second one of thethird pair of driving elements C2 has been depicted as terminating inlug element 2002. The pair of lug elements are coupled so as to belinearly displaceable with respect to each other. Suitably, the pair oflug elements are linearly displaceable along the direction y of the pairof driving elements to which they are attached. Suitably, the pair oflug elements are displaceable along a displacement axis that is parallelto and offset from the longitudinal axis 511 of the shaft. The lugelements 2001 and 2002 may be coupled by any suitable mechanism which isable to move the lug elements relative to each other along thedisplacement axis. For example, the lug elements may be coupled togetherby a screw 2003. The screw 2003 is captive in a first lug element 2002and constrained by the first lug element 2002 so as to prevent the screw2003 from displacing linearly with respect to the first lug element2002. For example, as shown in FIG. 20A, the screw may pass through ahole in the first lug element in which it is able to rotate, and beconstrained from linearly displacing through the first lug element bytwo portions 2004 and 2005 which have a larger diameter than the holethrough the first lug element. The screw 2003 is threaded through thesecond lug element 2001. Thus, the lug elements 2001 and 2002 displacelinearly towards each other when the screw is tightened, and displacelinearly away from each other when the screw is loosened.

FIG. 20B illustrates a further alternative tensioning mechanism. FIG.20B illustrates a further alternative arrangement of lug 1927 to thatshown in FIG. 19C. In the arrangement of FIG. 20B, the lug is utilisedin the tensioning mechanism. The lug of FIG. 20B has a pair of lugelements 2006 and 2007. One driving element of a pair of drivingelements terminates in one lug element, and the other driving element ofthe pair of driving elements terminates in the other lug element. Afirst one of the third pair of driving elements C1 has been depicted asterminating in lug element 2006, and the second one of the third pair ofdriving elements C2 has been depicted as terminating in lug element2007. The pair of lug elements are coupled so as to be linearlydisplaceable with respect to each other. Suitably, the pair of lugelements are linearly displaceable along the direction y of the pair ofdriving elements to which they are attached. Suitably, the pair of lugelements are displaceable along a displacement axis that is parallel toand offset from the longitudinal axis 511 of the shaft. The lug elements2006 and 2007 may be coupled by any suitable mechanism which is able tomove the lug elements relative to each other along the displacementaxis. For example, the lug elements may be coupled together by a screw2008. The screw 2008 is captive in a first lug element 2007 andconstrained by the first lug element 2007 so as to prevent the screw2008 from displacing linearly with respect to the first lug element2007. For example, as shown in FIG. 20B, the screw may pass through ahole in the first lug element in which it is able to rotate, and beconstrained from linearly displacing through the first lug element bytwo portions 2009 and 2010 which have a larger diameter than the holethrough the first lug element. The screw 2008 is threaded through thesecond lug element 2006. Thus, the lug elements 2006 and 2007 displacelinearly towards each other when the screw is tightened, and displacelinearly away from each other when the screw is loosened.

Referring to FIG. 19C, each instrument interface element 1905, 1906 and1907 is linearly displaceable parallel to the longitudinal axis of theshaft 511. The instrument interface element may be slideable along alinear rail. For example, first instrument interface element 1905 isslideable along rail 1928, second instrument interface element 1906 isslideable along rail 1929, and third instrument interface element 1907is slideable along rail 1930. Each instrument interface element can bedisplaced over a displacement range between a minimum displacementposition and a maximum displacement position. For example, the minimumand maximum displacement positions may be determined by the ends of therail along which the instrument interface element slides in thelongitudinal direction x of the shaft. The minimum and maximumdisplacement positions are labelled 1931 and 1932 on FIGS. 19B and 19Cfor the second and third instrument interface elements 1906 and 1907.The minimum and maximum displacement positions are labelled 1931 and1943 on FIG. 19B for the first instrument interface element 1905. Thefirst instrument interface element is linearly displaceable through amaximum distance d₁ minus the length of the first instrument interfaceelement in the direction x. The second instrument interface element islinearly displaceable through a maximum distance d₂ minus the length ofthe second instrument interface element in the direction x. The thirdinstrument interface element is linearly displaceable through a maximumdistance d₃ minus the length of the third instrument interface elementin the direction x. Suitably d₁<d₂ and d₁<d₃. Suitably, d₂=d₃.

Suitably, in the straight configuration of the instrument in which theend effector is aligned with the shaft, the first, second and thirdinstrument interface elements 1905, 1906 and 1907 are all located in thesame plane perpendicular to the longitudinal axis of the shaft.Alternatively, in the straight configuration of the instrument, thefirst instrument interface element 1905 may be centred in a differentplane to the plane in which the second and third instrument interfaceelements 1906, 1907 are centred. This is because the midpoint of thetravel of the first instrument interface element 1905 over d₁ is offsetfrom the midpoint of the travel of the second and third instrumentinterface elements 1906, 1907 over d₂, d₃.

Suitably, each instrument interface element comprises a body 1933, 1934,1935 and a lug 1927, 1936, 1937. The body 1933, 1934, 1935 is linearlydisplaceable between the minimum displacement position and the maximumdisplacement position of the instrument interface element. The pair ofdriving elements which engages the instrument interface element issecured to the lug of the instrument interface element. The lug islinearly displaceable within the body parallel to the direction alongwhich the body is displaceable. Suitably, the lug is linearlydisplaceable along the longitudinal direction x of the shaft parallel tothe longitudinal axis 511 of the shaft. The alignment mechanism adjuststhe displacement position of the body without displacing the lug. Forexample, the alignment mechanism may comprise a screw adjustmentmechanism coupled to the body and lug which enables the body to movewithout moving the lug. FIG. 19C depicts such a screw adjustmentmechanism. The body 1933, 1935 comprises a slot 1938, 1939 aligned withthe direction along which the body is displaceable. A screw 1940, 1941is threaded into the lug through the slot 1938, 1939. The screw 1940,1941 is constrained to slide along the slot. For example, the screw headmay be too large to pass through the slot and the screw body a loose fitthrough the slot. Thus, the when the screw is loose, the body isdisplaceable relative to the lug along the width of the slot. When thescrew is tight, the body is held fast with the lug. Thus, the relativeposition of the body and the lug can be adjusted by the width of theslot.

The following describes steps to be carried out during manufacturefollowing assembly of the instrument in order to set the tension of thedriving elements and the alignment of the instrument interface elements.

Initially, the instrument interface is loosened from the drivingelements. The instrument interface elements are set to the alignmentposition. For example, if the alignment position is with each instrumentinterface element at the mid-point of its travel over its displacementrange, then the instrument interface elements are aligned to thesepositions. This initial step may be a rough alignment of the instrumentinterface elements to their alignment positions. Alternatively, thisinitial step may not be carried out. Next, the end effector is placed inthe predetermined configuration. Next, the pairs of driving elements aretensioned. This may be done using any of the tensioning mechanismsdescribed herein, for example by sliding a tensioning pulley along arail or through a socket, or by displacing a pair of lug elements. Oncetensioned, the displacement position of the instrument interface elementis then set to the predetermined alignment position using the alignmentmechanism. For example, in the implementation shown in FIGS. 19A, 19Band 19C, the screw 1940, 1941 is loosened, and the body 1933, 1935 ofthe instrument interface element displaced along the rail 1930, 1929relative to the lug 1938, 1937 until the body of the instrumentinterface element is in the predetermined alignment position. The endeffector may be held in the predetermined configuration whilst the pairsof driving elements are tensioned. Alternatively, or additionally, theend effector may be returned to the predetermined configuration afterthe pairs of driving elements have been tensioned. The screw is thentightened.

FIGS. 21A, 21B and 21C illustrates a drive assembly interface 2100. Thedrive assembly interface is at the terminal end of the terminal link ofthe robot arm. That terminal link is connected to the link next to it bya roll joint. The roll joint permits the terminal link to rotate about alongitudinal axis 2104 of the terminal link. Drive assembly interface2100 comprises drive assembly interface elements 2101, 2102 and 2103.The drive assembly interface elements are configured to receiveinstrument interface elements 1905, 1906 and 1907. First drive assemblyinterface element 2102 is configured to receive first instrumentinterface element 1905. Second drive assembly interface element 2101 isconfigured to receive second instrument interface element 1906. Thirddrive assembly interface element 2102 is configured to receive thirdinstrument interface element 1907.

Each drive assembly interface element is displaceable along a directionparallel to the longitudinal axis 2104 of the drive assembly. Each driveassembly interface element is displaceable over a displacement range.When the instrument interface is seated in the drive assembly, as shownin FIG. 24, each drive assembly interface element is displaceable in thesame direction as the direction in which the instrument interfaceelement that it engages with is displaceable in.

The first drive assembly interface element 2102 engages the firstinstrument interface element 1905 on the longitudinal axis 2104 of thedrive assembly. Thus, the first drive assembly interface element 1905drives the first instrument interface element 1905 along thelongitudinal axis of the drive assembly, and hence along thelongitudinal axis of the terminal link of the robot arm. Suitably, ofall the drive assembly interface elements in the drive assembly, onlythe first drive assembly interface element 2102 is displaceable alongthe longitudinal axis 2104 of the terminal link. The first instrumentinterface element 1905 drives the first pair of driving elements A1, A2to drive rotation of the distal end of the instrument about the firstaxis 510 which is perpendicular to the instrument shaft axis 511. Whenthe instrument interface 1701 is seated in the drive assembly 2100, thelongitudinal axis 511 of the instrument shaft is parallel to thelongitudinal axis 2104 of the terminal link. Suitably, the longitudinalaxis 511 of the instrument shaft is coincident with the longitudinalaxis 2104 of the terminal link.

The second drive assembly interface element 2101 engages the secondinstrument interface element 1906 on an axis parallel to but offset fromthe longitudinal axis 2104 of the drive assembly. The second driveassembly interface element 2101 is displaceable along this axis so as todrive the second instrument interface element 1906 along this axis. Thesecond instrument interface element 1906 drives the second pair ofdriving elements B1, B2 to drive rotation of an end effector element 502about the second joint 507.

The third drive assembly interface element 2103 engages the thirdinstrument interface element 1907 on an axis parallel to but offset fromthe longitudinal axis 2104 of the drive assembly. The third driveassembly interface element 2103 is displaceable along this axis so as todrive the third instrument interface element 1907 along this axis. Thethird instrument interface element 1907 drives the third pair of drivingelements C1, C2 to drive rotation of the end effector element 503 aboutthe third joint 513.

Suitably, the drive assembly interface elements releasably engage thecorresponding instrument interface elements.

FIGS. 21A, 21B and 21C illustrate an exemplary mechanism for driving thelinear displacement of the drive assembly interface elements within thedrive assembly. Each drive assembly interface element 2101, 2102, 2103is driven by a respective threaded driveshaft 2105, 2106, 2107.Suitably, the first, second and third drive assembly interface elementsare independently driven by the driveshafts. A guide structureconstrains each drive assembly interface element, thereby preventing thedrive assembly interface element from rotating as the correspondingdriveshaft is rotated. For example, a guiderail constrains each driveassembly interface element, thereby preventing the drive assemblyinterface element from rotating as the corresponding driveshaft isrotated. The guiderails constrain the drive assembly interface elementssuch that the only motion that the drive assembly interface elements arepermitted to do is to move linearly parallel to the guiderail. The driveassembly interface elements may, for example, slide along theguiderails. In the implementation illustrated, the first drive assemblyinterface element 2102 and the second drive assembly interface element2101 are both constrained by the same guiderail 2108. The third driveassembly interface element 2103 is constrained by a different guiderail2109. In an alternative arrangement, the first and third drive assemblyinterface elements 2102 and 2103 are both constrained by the sameguiderail 2109. The second drive assembly interface element 2101 isconstrained by the guiderail 2108. In yet a further alternativearrangement, each drive assembly interface element is constrained by itsown guiderail. In another example, the guide structure is a guide slot,which constrains the motion of the drive assembly interface element suchthat it is only able to move linearly parallel to the guide slot. Aswith the guiderails, the guide slots are parallel to the longitudinaldirection 2104 of the drive assembly interface. The first drive assemblyinterface element 2102 is linearly displaceable through a maximumdistance s₁. The second drive assembly interface element 2101 islinearly displaceable through a maximum distance s₂. The third driveassembly interface element 2103 is linearly displaceable through amaximum distance S₃. Suitably s₁<s₂ and s₁<s₃. Suitably, s₂=s₃.

Suitably, in one configuration of the drive assembly, the first, secondand third drive assembly interface elements 2101, 2102 and 2103 are alllocated in the same plane perpendicular to the longitudinal axis 2104 ofthe terminal link. This configuration is the one depicted in FIGS. 21A,21B and 21C. All the drive assembly interface elements are centred on asingle cross section of the terminal link perpendicular to thelongitudinal axis 2104. Suitably, in this configuration, each driveassembly interface element is at the midpoint of its linear displacementover its displacement range. Suitably, this configuration is the defaultconfiguration that the assembly interface adopts when an instrument hasbeen removed from the robot arm. This configuration is arranged toreceive the instrument interface elements in their predeterminedalignment positions, described above. The predetermined alignmentposition may be the position at which each drive assembly interfaceelement is at the midpoint of its travel. The predetermined alignmentposition may be the position at which the centre points of all the driveassembly interface elements lie on the same plane.

In all configurations of the drive assembly, the second and third driveassembly interface elements 2101 and 2103 are both centred on a secondplane which is perpendicular to the plane that the first, second andthird drive assembly interface elements 2102, 2102 and 2103 are allcentred on in the configuration depicted in FIGS. 21A, 21B and 21C. Thissecond plane does not intersect the longitudinal axis 2104 of theterminal link. In all configurations, the first drive assembly interfaceelement 2102 is centred on a third plane which is parallel to but offsetfrom the second plane.

The drive assembly depicted in FIGS. 21A, 21B and 21C may drive theinstrument interface depicted in FIGS. 19A, 19B and 19C which in turndrives the first, second and third joints depicted in FIGS. 5A and 5B,such that the first drive assembly interface element 2102 drives thefirst joint 506, the second drive assembly interface element 2101 drivesthe second joint 507, and the third drive assembly interface element2103 drives the third joint 513. In an alternative arrangement, thedrive assembly interface elements may drive different joints. Forexample, if the first pair of driving elements A1, A2 are connected tothe second instrument interface element 1906, then the second driveassembly interface element 2101 drives the first joint 506. If thesecond pair of driving elements B1, B2 are connected to the firstinstrument interface element 1905, then the first drive assemblyinterface element 2102 drives the second joint 507. In this example, thethird pair of driving elements C1, C2 are connected to the thirdinstrument interface element 1907, so that the third drive assemblyinterface element 2103 drives the third joint 513. In this example, thefirst drive assembly interface element 2102 is linearly displaceablethrough a maximum distance s₁. The second drive assembly interfaceelement 2101 is linearly displaceable through a maximum distance s₂. Thethird drive assembly interface element 2103 is linearly displaceablethrough a maximum distance s₃. Suitably s₂<s₁ and s₂<s₃. Suitably,s₁=s₃.

Each instrument interface element comprises a body which is receivablein a corresponding socket of the drive assembly interface element. Theshapes of the body and socket correspond such that when the driveassembly interface element is displaced, this displacement istransferred to the instrument interface element without any slippage.Thus, the body fits snugly into the socket along at least one line inthe displacement direction. Suitably, the instrument interface elementis displaceable over the same displacement range as its correspondingdrive assembly interface element.

FIG. 22A illustrates an exemplary arrangement of the part of the body ofthe instrument interface element which is received in the socket of thedrive assembly interface element. The body comprises lower sidewalls2201 and 2202 which are separated by the length of the body in thedisplaceable direction x. The lower sidewalls are perpendicular to thedisplaceable direction x of the body. Upper sidewalls 2203 and 2204taper to a point 2205 from the lower sidewalls. Suitably, the uppersidewalls taper symmetrically to a point. On engaging the instrumentinterface with the drive assembly interface, the point 2205 is insertedinto the drive assembly interface element first, followed by the rest ofthe upper sidewalls 2203, 2204 and finally the lower sidewalls 2201,2202. The angle α at which the upper sidewalls meet is preferably lessthan or the same as 80°. By selecting α≦80°, the body will slide intothe socket when force is applied in the direction F as long as the pointis inside the socket, even if the body and socket are not fully alignedalong the displaceable direction x. The direction F is perpendicular tothe displaceable direction x. In other words, the direction F isperpendicular to the longitudinal axis of the shaft 504 andperpendicular to the longitudinal axis of the drive assembly.

FIG. 22B illustrates another exemplary arrangement of the part of thebody of the instrument interface which is received in the socket of thedrive assembly of the drive assembly interface element. The body is thesame as that described with reference to FIG. 22A except that it has aroller 2206 located on the point at which the two upper sidewalls meet.The roller 2206 is configured to rotate about an axis which isperpendicular to the displaceable direction x. The angle β at which theupper sidewalls meet may be greater than 80°. This is because the roller2206 aids seating of the body in the socket even if the body and socketare not fully aligned along the displaceable direction x when force isapplied in the direction F.

FIG. 22C illustrates another exemplary arrangement of the part of thebody of the instrument interface which is received in the socket of thedrive assembly of the drive assembly interface element. The body is thesame as that described with reference to FIG. 22A except that it has aroller 2207, 2208 located on each upper sidewall. The rollers 2207, 2208are configured to rotate about axes which are perpendicular to thedisplaceable direction x. The angle γ at which the upper sidewalls meetmay be greater than 80°. This is because the rollers 2207, 2208 aidseating of the body in the socket even if the body and socket are notfully aligned along the displaceable direction x when force is appliedin the direction F.

FIG. 23 illustrates an exemplary arrangement of a socket of a driveassembly interface element. The body comprises sidewalls 2301 and 2302which are separated by the length of the body in the displaceabledirection x. The sidewalls are perpendicular to the displaceabledirection x of the body. The sidewalls each terminate in a roller 2303,2304. The rollers 2303, 2304 are configured to rotate about axes whichare perpendicular to the displaceable direction x. The rollers 2303,2304 aid seating of the body in the socket even if the body and socketare not fully aligned along the displaceable direction x when theinstrument interface is applied to the drive assembly interface.

In one example, the length A of the body in the displaceable direction xis greater than the maximum distance the body is able to travel over thedisplacement range in the displaceable direction x. Suitably, the lengthA of the body in the displaceable direction x is greater than themaximum distance the socket of the drive assembly interface element isable to travel over its displacement range in the displaceabledirection. Thus, whatever displacement position the body has andwhatever displacement position the socket has, when the instrumentinterface is brought into engagement with the drive assembly interface,the body seats into the socket. Thus, no pre-alignment of the instrumentinterface elements and the drive assembly interface elements is requiredto cause the instrument interface and the drive assembly interface tomate. Suitably, the maximum distance the body is able to travel over itsdisplacement range is half the length of the body A/2. A is the lengthof the body.

Suitably, the maximum distance the socket is able to travel over itsdisplacement range is half the length of the body A/2.

In one example, the length B of the socket in the displaceable directionx is greater than the maximum distance the body is able to travel overthe displacement range in the displaceable direction x. Suitably, thelength B of the socket in the displaceable direction x is greater thanthe maximum distance the socket of the drive assembly interface elementis able to travel over its displacement range in the displaceabledirection. Thus, whatever displacement position the body has andwhatever displacement position the socket has, when the instrumentinterface is brought into engagement with the drive assembly interface,the body seats into the socket. Thus, no pre-alignment of the instrumentinterface elements and the drive assembly interface elements is requiredto cause the instrument interface and the drive assembly interface tomate. Suitably, the maximum distance the body is able to travel over itsdisplacement range is half the length of the socket B/2. B is the lengthof the socket. Suitably, the maximum distance the socket is able totravel over its displacement range is half the length of the socket B/2.

Suitably, the length A of the body in the displaceable direction isequal to the length B of the socket in the displaceable direction.

The instrument interface may have a guide bar to aid alignment andseating of the instrument interface into the drive assembly interfacewhen they are being brought into engagement. The guide bar is located onthe exterior face of the instrument interface which faces the driveassembly interface when they are brought into engagement. The guide baris received in the drive assembly interface prior to the instrumentinterface elements. Suitably, the guide bar is the first part of theinstrument interface to be received in the drive assembly interface asthey are brought into contact with each other. Once the guide bar hasbeen received in the drive assembly interface, it constrains therelative orientation with which the instrument interface and driveassembly interface are able to engage so as to align their longitudinalattitudes. Suitably, the guide bar only permits the instrument interfaceto seat fully into the drive assembly interface if the longitudinal axis511 of the instrument shaft is aligned with the longitudinal axis 2104of the terminal link of the robot arm.

Suitably, the guide bar is elongate, straight and parallel to thelongitudinal axis 511 of the instrument shaft. The guide bar may extendwholly across the instrument interface. For example, the guide bar mayextend in the longitudinal direction x from the end of the instrumentinterface which abuts the instrument shaft 504 to the opposing end ofthe instrument interface. Alternatively, the guide bar may extend in thelongitudinal direction x only over the longitudinal range bounded by theminimum and maximum displacement positions of the 1931, 1932 of theinstrument interface elements 1905, 1906, 1907. If the drive assemblyinterface and instrument interface are arranged such that they bothadopt their default predetermined alignment positions before beingbrought into engagement, then the guide bar may extend in thelongitudinal direction x only over the longitudinal range bounded by thedisplacements of the instrument interface elements in the predeterminedalignment positions. If in the predetermined alignment positions, theinstrument interface elements are all aligned in the same planeperpendicular to the longitudinal axis 511 of the instrument shaft, thenthe guide bar may extend in the longitudinal direction x only over theinstrument interface elements themselves. Suitably, the guide bar isnarrower than the diameter of the instrument shaft 504. The driveassembly receives the guide bar parallel to the longitudinal axis 2104of the drive assembly.

The guide bar may be formed of a single part, such as guide bar 1960shown in FIG. 19A. This illustrated guide bar extends across the wholelength of the instrument interface. The guide bar partially or whollyenvelops driving elements A1, A2, B1 and C1. In this way, the drivingelements are not exposed at the exterior of the instrument interface asthe instrument interface is brought into engagement with the driveassembly interface. The guide bar 1960 also stiffens the instrumentinterface.

Alternatively, the guide bar may comprise two or more parts. FIG. 25shows a view of the face of an instrument interface which first engageswith the drive assembly interface. Here, two guide bar parts 2501, 2502are shown. This guide bar extends in the longitudinal direction x acrosspart of the longitudinal range bounded by the minimum and maximumdisplacement positions of the instrument interface elements.

Both the guide bar and the first instrument interface element 1905 arereceived in the first drive assembly interface element 2102. The firstinstrument interface element comprises two body parts 1905 a and 1905 b,one of which is located on one side of the guide bar, and the other ofwhich is located on an opposing side of the guide bar. The first driveassembly interface element comprises two socket parts 2101 a and 2101 b,located on either side of the longitudinal axis 2104 of the driveassembly. As the instrument interface and the drive assembly interfaceare brought into engagement, the guide bar is received in the firstdrive assembly interface element first. The guide bar seats along thelongitudinal axis 2104 of the shaft between the two socket parts 2101 aand 2101 b. As the guide bar is received in the first drive assemblyinterface element 2101, it prevents the instrument interface fromtwisting as it is located in the drive assembly interface. The guide barcauses the attitudes of the drive assembly interface and the instrumentinterface to remain aligned as they engage. As the instrument interfaceis further lowered into the drive assembly interface, the first bodypart 1905 a engages the first socket part 2101 a on one side of theguide bar whilst the second body part 1905 b engages the second socketpart 2101 b on the opposing side of the guide bar.

It will be appreciated that the drive assembly interfaces describedherein could be modified to include further drive assembly interfaceelements to transfer drive to further instrument interface elements. Theinstrument interfaces described herein could be modified to includefurther instrument interface elements to transfer drive to furtherjoints of the articulation at the distal end of the instrument shaft.The articulation itself could also be modified to include furtherjoints.

It will also be appreciated that the end effector may only have one endeffector element. In this case, the articulation does not include thethird joint 513, the instrument interface does not include an instrumentinterface element for driving the third joint, and the drive assemblydoes not include a drive assembly interface element for driving thatinstrument interface element.

The instrument could be used for non-surgical purposes. For example itcould be used in a cosmetic procedure.

The applicant hereby discloses in isolation each individual featuredescribed herein and any combination of two or more such features, tothe extent that such features or combinations are capable of beingcarried out based on the present specification as a whole in the lightof the common general knowledge of a person skilled in the art,irrespective of whether such features or combinations of features solveany problems disclosed herein, and without limitation to the scope ofthe claims. The applicant indicates that aspects of the presentinvention may consist of any such individual feature or combination offeatures. In view of the foregoing description it will be evident to aperson skilled in the art that various modifications may be made withinthe scope of the invention.

1. A robotic surgical instrument comprising: a shaft; an articulation ata distal end of the shaft for articulating an end effector, thearticulation driveable by pairs of driving elements; and an instrumentinterface at a proximal end of the shaft, the instrument interfacecomprising an internal portion which is within the projected profile ofthe shaft and an external portion which is outside of the projectedprofile of the shaft, the instrument interface comprising instrumentinterface elements for driving pairs of driving elements, wherein afirst instrument interface element engages a first pair of drivingelements in the internal portion.
 2. A robotic surgical instrument asclaimed in claim 1, wherein between the proximal end of the shaft andthe first instrument interface element, the first pair of drivingelements lies wholly within the internal portion.
 3. A robotic surgicalinstrument as claimed in claim 1, wherein between the proximal end ofthe shaft and the first instrument interface element, the first pair ofdriving elements is wholly parallel to the longitudinal axis of theshaft.
 4. A robotic surgical instrument as claimed in claim 1, whereinthe first pair of driving elements emerge from the proximal end of theshaft and engage the first instrument interface element without beingconstrained to move around any intermediate pulleys between the proximalend of the shaft and the first instrument interface element.
 5. Arobotic surgical instrument as claimed in claim 1, wherein the firstpair of driving elements is fast with the first instrument interfaceelement such that a displacement of the first instrument interfaceelement is transferred to the first pair of driving elements.
 6. Arobotic surgical instrument as claimed in claim 1, wherein only thefirst instrument interface element engages the first pair of drivingelements in the internal portion, the remainder of the instrumentinterface elements engaging their associated pairs of driving elementsin the external portion.
 7. A robotic surgical instrument as claimed inclaim 1, the articulation comprising a first joint driveable by thefirst pair of driving elements, the first joint permitting the endeffector to rotate about a first axis transverse to a longitudinal axisof the shaft.
 8. A robotic surgical instrument as claimed in claim 1,wherein the first instrument interface element is linearly displaceablealong a displacement axis parallel to the longitudinal axis of theshaft.
 9. A robotic surgical instrument as claimed in claim 1, wherein asecond instrument interface element engages with a second pair ofdriving elements in the external portion, the second pair of drivingelements constrained to move around a first pulley arrangement betweenthe proximal end of the shaft and the second instrument interfaceelement.
 10. A robotic surgical instrument as claimed in claim 9,wherein the second pair of driving elements is fast with the secondinstrument interface element such that a displacement of the secondinstrument interface element is transferred to the second pair ofdriving elements.
 11. A robotic surgical instrument as claimed in claim9, wherein the articulation comprises a second joint driveable by thesecond pair of driving elements, and the end effector comprises an endeffector element, wherein the second joint permits the end effectorelement to rotate about a second axis transverse to the first axis. 12.A robotic surgical instrument as claimed in claim 9, wherein the secondinstrument interface element is linearly displaceable along adisplacement axis parallel to the longitudinal axis of the shaft.
 13. Arobotic surgical instrument as claimed in claim 9, wherein the firstpulley arrangement comprises a pair of pulleys, the second pair ofdriving elements emerging from the pair of pulleys in a directionparallel to and offset from the direction the second pair of drivingelements emerges from the proximal end of the shaft.
 14. A roboticsurgical instrument as claimed in claim 1, wherein a third instrumentinterface element engages with a third pair of driving elements in theexternal portion, the third pair of driving elements constrained to movearound a second pulley arrangement between the proximal end of the shaftand the third instrument interface element.
 15. A robotic surgicalinstrument as claimed in claim 14, wherein the third pair of drivingelements is fast with the third instrument interface element such that adisplacement of the third instrument interface element is transferred tothe third pair of driving elements.
 16. A robotic surgical instrument asclaimed in claim 14, wherein the articulation comprises a third jointdriveable by the third pair of driving elements, and the end effectorcomprises a further end effector element, wherein the third jointpermits the further end effector element to rotate about the secondaxis, and wherein the third instrument interface element is linearlydisplaceable along a displacement axis parallel to the longitudinal axisof the shaft.
 17. A robotic surgical instrument as claimed in claim 14,wherein the second pulley arrangement comprises a pair of pulleys, thethird pair of driving elements emerging from the pair of pulleys in adirection parallel to and offset from the direction the third pair ofdriving elements emerges from the proximal end of the shaft.
 18. Arobotic surgical instrument as claimed in claim 14, wherein in oneconfiguration of the robotic surgical instrument, the first instrumentinterface element, the second instrument interface element and the thirdinstrument interface element are all centred on the same planeperpendicular to the longitudinal axis of the shaft.
 19. A roboticsurgical instrument as claimed in claim 18, wherein the first instrumentinterface element, the second instrument interface element and the thirdinstrument interface element are all centred on the same planeperpendicular to the longitudinal axis of the shaft in a straightconfiguration of the robotic surgical instrument in which the endeffector is aligned with the shaft.
 20. A robotic surgical instrument asclaimed in claim 18, wherein the first instrument interface element islinearly displaceable through a maximum distance d₁, the secondinstrument interface element is linearly displaceable through a maximumdistance d₂, and the third instrument interface element is linearlydisplaceable through a maximum distance d₃, wherein d₁<d₂ and d₁<d₃.